Introduced, or nonindigenous, species
are a major threat to biodiversity worldwide. Large estuaries and embayments
are particularly vulnerable to colonization by new species. Over 230 nonindigenous
species have established themselves in the San Francisco Bay estuary.
Not only do these exotic invaders displace native species, they also alter
habitat structure and energy flow through ecosystems. For example, the
Atlantic marsh grass
Spartina alterniflora spreads by runners
and traps sediment in its roots. Over time, this invader can transform
a mudflat to a high marsh. The European green crab Carcinus maenas
preys on small native clams, worms and juvenile flatfish and competes for
food with native crabs, fishes and migratory seabirds.

How do these nonindigenous
species get to our shores?

While aquaculture species such as
the Japanese oyster, Crassostrea gigas, were introduced intentionally,
they also brought with them many undesirable hitchhikers, including oyster
drills. Bait worms and lobsters from the Atlantic are routinely shipped
to the west coast wrapped in seaweed that harbors many small organisms,
including snails and young green crabs. Once the seaweed is discarded into
our bays, these foreign species can take up residence and establish new
populations. Commercial ships, transporting large volumes of ballast water
from one port to another, act as vectors for introducing planktonic organisms.
The purple varnish clam, Nuttallia obscurata, was probably
transported in ballast water from Japan to British Columbia before 1993.
By 1997, it spread to Oregon, presumably via natural transport of larvae
by ocean currents. Unlike chemical pollutants, introduced species reproduce
and once established, are extremely difficult, if not impossible, to remove.

Who are the Invaders in Oregon Estuaries?

Our goal is to summarize the present
knowledge of nonindigenous species in Oregon estuaries. The list of exotic
species is primarily based on surveys conducted by Jim Carlton (Coos Bay),
John Chapman (Columbia River and other estuaries) and the US Environmental
Protection Agency (Yaquina Bay). These studies provide evidence that well
over
100 invaders have become established in Oregon's estuaries.
It should be noted, however, that this figure is an underestimate because
most estuaries, habitats and taxonomic groups have not been systematically
sampled.
For more information see:

This web page was created by Sylvia Behrens Yamada in November 2001 and updated in November 2003.
Send your comments for the next version of Introduced Species in Oregon
Estuaries to:
yamadas@science.oregonstate.edu